Thank you, callsign kilo.
In Boeing´s Aeromagazine No.16 it says: ..."
Polar navigation option.
These latitude limitations
on flight operation do not
apply to 747-400, 777, and
737-600/-700/-800/-900
airplanes equipped with
the polar navigation option
(heading reference switch
and FMC Update U10.3 or
later) and dispatched with
the following equipment
operational: CDU, left
GPS, both IRUs in navigation
(NAV) mode, and both display
electronic units.
Flight crews of such equipped airplanes
should not use HDG SEL or ROLL CWS
north of 89 deg 30 min north latitude
or south of 89 deg 30 min south latitude.
They also should not use the heads-up
display system, if installed, when the
heading reference switch is in TRUE.
So, any comment would be appreciated.
Thanks again.
Chris